To some extent, the distinction between “ketogenic” and “low-carb, high-fat” is negligible. Any diet low enough in carbohydrate to be meaningful is going to be ketogenic.
The point to remember is that your carbohydrate threshold is unique. Some of us can tolerate more carbohydrate (by weight) than others. The 20 g/day limit promoted on these forums is low enough that practically everyone, except people who are severely metabolically damaged, can get into ketosis at that level. Carbohydrates are, for the most part, nothing more than strings of glucose molecules, which get severed in the digestive tract and sent, via the portal vein, as glucose to the liver to be managed. Glucose above a certain amount needs to be removed from the blood stream, to prevent the damage that hyperglycaemia can cause. The rise in serum glucose causes the pancreas to secrete insulin, which drives the excess glucose into muscles to be metabolised and into adipose tissue to be stored as fat.
Unless you eat below your carbohydrate threshold, your serum insulin is going to remain elevated, preventing fat from leaving the adipose tissue to be metabolised. If 100 g/day of carbohydrate keeps you out of ketosis, then you are not going to experience the benefits of a low-carb keto diet, such as reversal of Type II diabetes and reduction in stored fat.
It has been demonstrated using radio-labeled food that it is the carbohydrate we eat that ends up as fat in the adipose tissue. The fat we eat, especially the monounsaturated fat, gets metabolised. This is the reason we stress replacing the carbohydrate you have eliminated from your diet with eating fat to satiety. Fat is more calorie-dense than carbohydrate, so it takes less to satisfy us, and it also has the benefit of barely stimulating insulin at all (just enough to keep us alive). This makes it a “safe” source of calories, especially from the point of view of fat loss. It has been demonstrated that eating to satiety on a well-formulated ketogenic diet promotes the proper functioning of the appetite hormones, making the appetite a reliable guide to how much food to eat. People with excess fat to lose who eat a ketogenic diet to satiety find their appetite naturally regulating their food intake to a level that lets the body metabolise both the fat they eat and the excess stored fat that the body does not need. In fact, it has been shown that people can eat a considerably higher calorie count than they actually need, and the body will respond by ramping up the metabolism, creating waste heat, dumping calories in urine, etc. Conversely, eating too little food causes the body to lower the metabolism and shut down non-essential functions (such as hair and nail growth, and the reproductive system) until the famine is over, and food is once more abundant.